1. Field of the Invention
The present invention relates to a method for cutting out a hard-brittle substrate and a cutout device suitable for use in the method, and more particularly to a method and a device for cutting out various substrates from a plate material having hard-brittleness such as glass, quartz, sapphire, ceramics or a silicon wafer for cutting out a substrate such as a glass substrate or a protective cover for a liquid crystal display screen and the like mounted on a personal digital assistance such as a mobile phone, a smartphone or a tablet PC, a digital camera, a portable game machine or other various products from a glass plate (mother glass to be described later).
It should be noted that the “substrate” as employed herein refers to a plate-shaped part on which a functional component is arranged in order to implement some function. More specifically, the “substrate” herein means not only those commonly called “substrates” such as a glass substrate for a liquid crystal display and the like or a substrate made of glass for a magnetic hard disk, but also a cover glass and the like for a cover glass integrated type touch panel and the like provided in a mobile phone and the like and configured to perform the function of protecting a liquid crystal display device and the like disposed on the back side of the cover glass in the touch panel and the like.
2. Description of the Related Art
Glass substrates as a typical example of a hard-brittle substrate are used as substrates for a display of a liquid crystal television or a personal computer, a display of a personal digital assistance such as a mobile phone, a smartphone or a tablet PC, a display of a digital camera, and a flat-panel display for use in other various equipment, and are used as a protective cover for protecting such a display. Besides, glass substrates are also used as the substrate for the above-described hard disk and the like because of having a lower coefficient of expansion and higher shock resistance than a conventional substrate made of aluminum. Thus, the industrial applications of glass substrates are being expanded.
A general practice for obtaining such a glass substrate is to cut out plural substrates from a large-sized glass plate called mother glass. A method for cutting out the substrates typically involves a combination of processes called “scribing” and “breaking.” The scribing is a process of making cuts in the mother glass in accordance with the shapes of the substrates to be cut out. The breaking is a process of cutting off the substrates from each other or cutting off the substrates from margins (borders) by applying a bending force to the glass plate in accordance with the cuts made by the scribing.
In this connection, examples of the scribing include scribing by mechanically making cuts by a diamond chip or a diamond roller and the like, and laser scribing utilizing the development of cracks by laser-induced thermal stress by laser irradiation of the glass plate. The laser scribing enables non-contact processing of the glass plate. In addition, the laser scribing can prevent contamination of a workpiece without generating glass cutting powder and the like, and can also prevent deterioration in strength of the glass without developing microcracks in broken and divided surfaces. Thus, cutting out with the laser scribing is coming into general use for the cutting out of the glass substrates in the aforementioned fields such as a flat-panel display.
Here, the cutting out with the already known laser scribing also needs the breaking after the scribing. However, such cutting out has difficulty in high-precision control of the breaking direction and the like of a glass plate during the breaking process, and an end face formed on the glass after the breaking does not always have a cross section with high precision. These problems hinder the use of the laser scribing for cutting out a minute substrate, the cutout of a substrate having a curved line, or the cutting out of a substrate from multilayer structure glass, somewhat thick plate glass, reinforced glass and the like. Taking this hindrance into account, there has also been a proposal of laser scribing called “full cut,” which enables the laser scribing to form scribing not only in the vicinity of a surface of a glass plate but also throughout the thickness of the plate, thereby eliminating the need for a breaking process (refer to Japanese Patent KOKAI (LOPI) No. 2006-256944).
Meanwhile, blasting which involves ejection of abrasive grains together with compressed gas against a surface to be processed of a workpiece is publicly known as a type of cutting, and there has also been a proposal of the use of such blasting for formation of barrier ribs (formation of grooves) in a glass substrate for a plasma display panel (refer to Japanese Patent KOKAI (LOPI) No. 2000-215795).
Although the cutout of a substrate by the above-described laser scribing needs the introduction of an expensive laser scribing apparatus and hence needs a lot of initial investments, the cutting out by this method is commonly said to have the advantage of eliminating a need for a mechanical polishing operation for an end face of a cut-out substrate, because the cutting out causes no microcrack development in the end face of the cut-out substrate and, moreover, forms the end face into a mirror surface.
Even if the end face of the cut-out substrate is the mirror surface, however, a brittle glass substrate is very easily damaged in its portions having a sharp shape including edges or corner portions formed on its periphery.
Therefore, cracks such as large or small cracks or chipped sections tend to occur in the edges or the corner portions of substrates by contact of one substrate with another or contact with working tools and the like during transportation or during processing. Occurrence of such cracks or chipped sections will be collectively referred to as “chipping” hereinafter. Once such chipping occurs in a substrate, the substrate is fractured from the position of the chipping merely by applying a slight force in a bending direction.
Also, a substrate having sharp edges or corner portions remaining therein is dangerous and hence needs careful handling during assembly operation and the like. In addition, the obtained substrate also involves the risk of injuring a user, if the substrate is mounted in such a way that the edges or corner portions of the substrate assembled in a final product may come into contact with the user's hands or fingers, such for example as when the substrate is used as a cover glass for a liquid crystal display screen and the like.
In almost all cases, therefore, even the substrate cut out by the laser scribing needs an operation, such as what is called “light-chamfering” or “chamfering,” for removing the edges or the corner portions by subjecting a peripheral portion of the cut-out substrate to mechanical polishing and the like. Among advantages commonly said for the laser scribing, the advantage of eliminating the need to polish the end face can be enjoyed in rather limited situations.
In contrast, if blasting is used for cutting out a brittle material substrate such as glass, a blasting apparatus of relatively simple structure can be used for cutting out. Having no need to introduce expensive equipment such as the laser scribing apparatus, the cutting out with the blasting is expected to start with low initial investments.
Although a conventional art in which the blasting is used to form the barrier ribs in the glass substrate for the plasma display panel is existed as mentioned above (refer to Japanese Patent KOKAI (LOPI) No. 2000-215795), the blasting has not been applied to “cut out” a glass substrate so far. The possible reason why the blasting is not used to cut out the glass substrate as described above is that etching by the blasting cannot be used for scribing.
Specifically, even if grooves are formed by blasting in a surface of mother glass in accordance with the shape of substrates to be cut out in order to perform breaking along the grooves, the grooves formed by the blasting are round at their bottom surfaces unlike V-shaped cuts formed by a diamond chip or a diamond roller and the like. For this reason, the mother glass is not easily broken and cut even with the application of a force to the mother glass in the bending direction. Or, even if the mother glass can be broken and cut, the mother glass cannot necessarily be cut with precision along the grooves formed by the blasting. Hence, the blasting cannot be used instead of the already known scribing.
Therefore, the use of the blasting for cutting out the glass substrate needs cutting such that the grooves are formed not only in the vicinity of the surface of the mother glass but also throughout the thickness of the mother glass until the grooves pass through the mother glass.
Under the above preconditions, in order to further verify the possibility of the use of blasting for cutting out a glass substrate, the inventor of the prevent invention made an attempt to cut out substrates by laying out the cutout positions of substrates 120 on a mother glass 100 as illustrated in FIG. 8, masking the mother glass by adhesively bonding blast-resistant protective films 104 to the layout positions of the substrates 120 on one surface alone or front and back surfaces of the mother glass, and cutting away the mother glass 100 in portions where the protective films 104 are not attached, by ejecting abrasive grains together with compressed air from an ejection nozzle.
However, when the blasting was continuously performed to complete such cutting, cracks 131 developed as illustrated in FIG. 8 in a margin 130 (a portion commonly called a “border”) formed on the outer periphery of the layout positions of the substrates, accordingly, the substrates cannot be cutout.
Moreover, in the case of the cutting by the blasting from the front and back surfaces of the mother glass 100, an operation for turning over the mother glass 100 or doing the like is necessary in the course of processing. In this case, even if the margin 130 can be prevented from becoming cracked during the blasting, a force in the bending direction is applied to the mother glass 100 in the course of turning over the mother glass 100, and the mother glass 100 breaks from a thinned portion.
As described above, although the cutting by the blasting is expected to enable the cutout of a hard-brittle material substrate with low initial investments because the blasting can be implemented with a simpler apparatus configuration than the laser scribing apparatus and the like, simple application of the blasting to the cutout of the glass substrate resulted merely in causing damage to the mother glass.
The above description is provided for the cutout of the glass substrate as an example of the brittle material substrate, however the same problem arises also with a plate material such as quartz, sapphire, ceramics or a silicon wafer which is hard and brittle like glass, and the cutout of the substrate is not possible with the simple application of the blasting.
Therefore, an object of the present invention is to provide a cutout method capable to cut out a brittle material substrate without causing damage to a plate material made of a hard-brittle material during operation by blasting which has not hitherto been used as a method for cutting out the brittle material substrate, such as the cutout of a glass substrate for a personal digital assistance or a flat-panel display, and to provide a cutout device suitable for use in cutout by the method.